Learning is a fundamental property of the brain. In many instances, learning is a positive attribute and it allows groups of neurons to acquire selective responses. The responses of a group of neurons to a given stimulus is called a "central representation", and these exist throughout the brain for processing complex sensory stimuli, or planning and executing complex movements. In other instances, the natural learning mechanisms of the brain are co-opted by noisy or abnormal inputs, leading to disintegration of the central representations that create normal sensation and action. The cerebral cortex has been widely implicated in learning for both sensation and action, and the cellular mechanisms that allow neurons to have plasticity are well known. This Program Project has the long-term goal of understanding how these mechanisms act at a system level to create circuits of neurons that are capable of supporting normal sensation and action. A related long-term goal is to understand how abnormal inputs cause degraded representations, how those degraded representations contribute to neurological disorders, and how to reconstruct order in central representations to relieve the disorders. Four projects support interacting approaches to these long-term goals on four different behavioral systems that rely heavily on the function of the cerebral cortex. Project 1 will continue an investigation of the cortical and cerebellar sites and mechanisms of learning in smooth pursuit eye movements. Project 2 will extend previous analysis of learning to recognize and emit one's own song in the auditory forebrain of song birds. It will investigate learning in earlier auditory areas that are homologous to the different levels of processing in the hierarchy of auditory cortex of mammals. Project 3 will also how speech sounds are represented in the brains of awake primates, and will investigate how the representation is altered when individuals are trained to discriminated different sounds. Project 4 will extend a prior analysis of the sensory correlates of focal dystonia into the motor cortex, and will study a similar dystonia that can be created in the auditory system by providing noise as a primary acoustic stimulus. These studies will elucidate the brain's natural learning abilities and provide new insight into how those abilities might be used to treat neurological disorders arising from abnormal central representations of sensory or motor information.